1. Field of the Invention
This invention relates to a switch mechanism and, in particular, to a thermally responsive switch useful as a flame switch and the like in a burner system.
2. Brief Statement of the Prior Art
Various devices have been designed for flame detection at a pilot burner in the burner assembly of heating appliances such as furances, water heaters and the like. Some of these devices have employed a thermally responsive unit having an outer metal tube and an inner metallic or ceramic rod. One end of this unit is secured to a switch housing with its opposite end interconnected so, when heated, a differential thermal expansion occurs between the outer tube and the inner rod. The inner rod is connected through various mechanisms to the switch blade of a switch mechanism. Typically, the device includes a spring to bias the switch in a normally off position in the event of failure of the thermally responsive unit. Typical of this device is that which is described in U.S. Pat. Nos. 3,194,927 and 3,310,047.
Another, similar type is described in U.S. Pat. No. 3,235,691. Each of the foregoing devices have a clutch mechanism between the thermally responsive unit and the switch mechanism, thereby accomodating for thermal expansion in excess of that necessary to operate the switch contacts.
The aforedescribed switch mechanisms must be individually calibrated and use elements which are not readily adaptable to mass manufacture with simple machine operations such as stamping, punching and the like. The devices also have a high maintenance requirement since their thermal response changes during use by fatigue of metal parts, formation of metal oxide surfaces, etc.